Radio frequency repeaters have been used for many years in connection with various types of communication systems. Many of the known prior repeater systems were intended to be permanently mounted at a fixed location and to received signals from and transmit signals to other fixed locations.
Repeater or booster circuits are also known for use in connection with cellular mobile radio telephone systems. One such repeater is disclosed in copending and commonly assigned U.S. patent application Ser. No. 081,120 entitled BOOSTER filed Aug. 3, 1987 now U.S. Pat. No. 4,941,200. The disclosure and figures of that application are incorporated herein by reference.
Two problems have been noted with prior art booster systems used in a cellular radio telephone environment. In one instance, the mobile units can physically approach the booster and as a result thereof supply to the booster a continually increasing input signal. This can result in the booster transmitting signals received from the mobile at excessively high power levels.
A mobile driving in close to the booster can exceed the input range of the booster If this happens, the RSSI signal level measuring circuitry may no longer function properly. As a result, the booster output exceeds a maximum output desired threshold. When this happens, booster circuitry reacts as if the excessive output is due to an oscillation condition and therefore permanently reduces gain. Thus, any mobile which drives to within overload range of the booster could permanently impair booster operation.
In addition, if the gain of the booster should be set too high for the surrounding conditions, an oscillatory condition can result. Hence, it would be desirable to be able to limit the transmitter output power when a mobile unit comes close to the booster. It would also be desirable to be able to automatically reduce the gain of the booster, should oscillation take place, so as to terminate the oscillatory condition.